Field
Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to providing radio frequency impairments correction with respect to wireless communications.
Background
Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, and the like. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the Universal Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). Examples of multiple-access network formats include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks.
A wireless communication network may include a number of base stations or node Bs that can support communication for a number of user equipments (UEs). A UE may communicate with a base station via downlink and uplink. The downlink (or forward link) refers to the communication link from the base station to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the base station.
A base station may transmit data and control information on the downlink to a UE and/or may receive data and control information on the uplink from the UE. On the downlink, a transmission from the base station may encounter interference due to transmissions from neighbor base stations or from other wireless radio frequency (RF) transmitters. On the uplink, a transmission from the UE may encounter interference from uplink transmissions of other UEs communicating with the neighbor base stations or from other wireless RF transmitters. This interference may degrade performance on both the downlink and uplink.
As the demand for mobile broadband access continues to increase, the possibilities of interference and congested networks grows with more UEs accessing the long-range wireless communication networks and more short-range wireless systems being deployed in communities. Research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications.
Radio frequency (RF) links, whether in the uplink (UL) or downlink (DL), suffer from linear and non-liner distortions resulting in error vector magnitude (EVM) in a received signal, and in power leakage to the adjacent channels. For example, the impairments with respect to any particular RF link may comprise non-linear distortions, such as due to operation of the transmit power amplifiers (PAs), as well as from linear distortions, such as due to the propagation channel (e.g., liner time invariant (LTI) impairments of the propagation channel).
Although attempts have been made to mitigate the RF link impairments, the prior solutions are not optimal in the sense of the whole non-linear (i.e., linear+non-linear) channel. The existing solutions rely on addressing the RF link impairments by using two independent digital blocks. The first such digital block is a linear precoder that is responsible for maximal exploitation of the capacity of the liner propagation channel. The second such digital block is a digital predistorter (DPD) that is responsible for predistortion, with appropriate back-off (BO), of the non-linear distortions (e.g., the non-linearities of the power amplifiers (PAs)), in order to keep the total channel as linear as possible. A significant drawback of such an approach is expressed in the requirement of high BO, resulting in low power efficiency of the power amplifier (PA) and lower emission power. The BO is used not only due to the signal quality considerations, but also to maintain a predefined adjacent channel power leakage ratio (ACLR).